Alkylating agents are among the most useful and extensively used anticancer agents;they occupy a central position in cancer chemotherapy. Our laboratory has designed and synthesized a new class of tumor inhibitory prodrugs, the 1,2-bis(sulfonyl) hydrazines, which generate through activation reactive electrophilic structures that cross-link DNA. Preclinical studies have shown that 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)- 2-[(methylamino)carbonyl]hydrazine, designated Cloretazine, is therapeutically superior to other 1,2- bis(sulfonyl) hydrazines and to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), which like Cloretazine are biological chloroethylating agents, against a variety of transplanted murine and human tumors. Cloretazine also readily crosses the blood brain barrier, is active both orally and parenterally, is not cross-resistant with cyclophosphamide, BCNU, or melphalan, and a by-product of its activation, methyl isocyanate, has synergistic cytotoxic activity with the generated chloroethylating species. Methyl isocyanate functions in part by inhibiting O6-alkylguanine-DNA alkyltransferase activity (AGT), a major mechanism of resistance to agents such as Cloretazine, which alkylate the O-6 position of guanine in DNA. Methyl isocyanate also enhances the cytotoxicity of the chloroethylating species generated from Cloretazine in cell lines devoid of AGT indicating that methyl isocyanate produces other metabolic lesions. Cloretazine has shown significant antileukemic activity against adult AML in Phase I and II clinical trials;it is presently in a Phase III trial in combination with AraC in adult AML and in Phase II trials in adult and pediatric glioblastoma. A second 1,2-bis(sulfonyl)hydrazine, 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[[1- (4-nitrophenyl) ethoxy] carbonyl]hydrazine, designated KS119, with selective activation by and kill of hypoxic cells of solid tumors, is in preclinical development. The Specific Aims of this application include continued studies on the mechanism(s) of action of Cloretazine and KS119 and also (a) the synthesis of analogs of Cloretazine designed to circumvent the resistance afforded by AGT, and analogs designed to release increased quantities of the methyl isocyanate to enhance the chloroethylating properties of Cloretazine;(b) the synthesis of analogs of KS119 and water-soluble derivatives thereof that not only release an alkylating species but also of methyl isocyanate upon activation;and (c) a comparison of the mechanism(s) of action of newly synthesized 1,2-bis(sulfonyl)hydrazines to ensure preclinical superiority of newly developed second generation agents. These studies will include measurements of antitumor efficacy against a broad spectrum of transplanted tumors, of toxicity, pharmacological disposition, cross-linking and repair of DNA, and the capacity to inhibit AGT. These investigations should lead to optimization of the anticancer potential of the 1,2-bis(sulfonyl)hydrazine prodrugs.